It is generally understood that a television is designed to receive and display low resolution, high intensity data while computer monitors are designed to display high resolution, low intensity images. As such, when video images designed for display on a television are displayed on a computer monitor, they appear dull in comparison to when displayed on a television. Similarly, when an image designed for display on a computer display is presented on a television, it looks slightly surreal and slightly distorted.
The distortion in the shape of the graphics data (i.e., data formatted for display on a computer monitor) occurring on a commercial grade television is called blooming. The effects of blooming cause the width of a graphics image to be wider than desired. This typically occurs because a graphics image has a very high average brightness, typically above ninety percent (90%), whereas an average television signal has an average brightness in the range of fifty to seventy percent. Consumer grade televisions are not designed to handle such high brightness signals, resulting in the distortion of the graphic images. Note that high-end televisions do not experience blooming since they are designed to receive video signals that span the entire contrast range (0%-100%). The high-end televisions, however, cost at least twice that of consumer grade televisions.
One solution to reducing the blooming effect when displaying graphic images (e.g., GUI graphics, windows) on a television set is to simply lower the maximum contrast allowed. For example, the maximum contrast may be set to be seventy-five percent (75%) of the total contrast range, insuring that blooming will not occur. This approach works fairly well for graphical images such as windows that contain text, however, it does not work well with displaying DVD images. Because of the reduced contrast, the overall intensity of the DVD images are reduced producing a dull image, especially when compared to the DVD images being displayed on a television. As such, this is an undesirable technique for displaying DVD images.
Another technique for automatic adjusting of the contrast of the television is done based on the ambient lighting of the environment in which a television resides. As ambient lighting decreases, the average brightness of a signal is reduced. Conversely, when the ambient light increases, the average brightness of the signals increases. This automatic adjusting technique, however, was not based on the content of the images being displayed. As such, this technique would not resolve the blooming effect of displaying graphics images on a television.
Therefore, a need exists for a method and apparatus that provides for control of contrast of images based on the image content.